Frequency of climbing behavior as a predictor of altered motor activity in rat forced swimming test

Previous work has shown that the frequency of climbing behavior in rats submitted to the forced swimming test (FST) correlated to the section's crosses in the open field test, which suggest it might be taken as a predictor of motor activity in rat FST. To investigate this proposal, the frequency, duration, as well as the ratio duration/frequency for each behavior expressed in the FST (immobility, swimming and climbing) were compared in animals treated with a motor stimulant, caffeine (CAF), and the antidepressant, clomipramine (CLM). Male Wistar rats were submitted to 15 min of forced swimming (pre-test) and 24 h later received saline (SAL, 1 ml/kg, i.p.) or CAF (6.5 mg/kg, i.p.) 30 min prior a 5-min session (test) of FST. To validate experimental procedures, an additional group of rats received three injections of SAL (1 ml/kg, i.p.) or clomipramine (CLM, 10 mg/kg, i.p.) between the pre-test and test sessions. The results of the present study showed that both drugs, CLM and CAF, significantly reduced the duration of immobility and significantly increased the duration of swimming. In addition, CAF significantly decreased the ratio of immobility, and CLM significantly increased the ratio of swimming and climbing. Moreover, CLM significantly increased the duration of climbing but only CAF increased the frequency of climbing. Thus, it seems that the frequency of climbing could be a predictor of altered motor activity scored directly in the FST. Further, we believe that this parameter could be useful for fast and reliable discrimination between antidepressant drugs and stimulants of motor activity.